1. Field of the Invention
This invention relates to a tubing rotator assembly that sits inside a casing head for purposes of suspending and rotating the tubing string in an oil well.
2. Brief Description of Prior Art
A typical wellhead is often comprised of a casing head which engages or is otherwise mounted to a casing string contained within a wellbore of a well at the surface. A mandrel bowl is mounted to the casing head and provides a support mechanism for the tubing string which is contained within the wellbore.
The production of fluids from an oil and gas well often involves the use of a downhole pump that can pump fluids to the surface through the tubing string. This downhole pump is often mechanically actuated through the use of a rod string located within the tubing string. The rod string is usually reciprocated up and down at the surface or, rotated at the surface to impart motion on the pump. The reciprocation or rotation of the rod string causes the rods to wear against the tubing, which may cause the tubing string to wear thin and develop a hole in the tubing. This wear action also wipes off chemical inhibitors that may be placed into a well to minimize corrosion of the tubing and rods by the production fluids. Thus, the wear action can also lead to tubing holes due to corrosion since the inhibitors are wiped off. These wear related holes in the tubing causes inefficient lift or no lift of the fluids to the surface and typically requires a rig to service the well. Reducing the failure frequency of the tubing strings will not only reduce operating costs but also will allow additional oil to be developed by reducing the economic production rate limit of each well.
Since 1927, several patents have been obtained on variations to tubing rotators that generally rotate the tubing manually or automatically to attempt to reduce the frequency of tubing holes developed due to the wearing action of the rods. Conventional casing heads are not typically able to be retrofitted to accommodate the necessary structure of a tubing rotator. Further, the tubing rotators of the prior art typically use gears and drive assembly to rotate the tubing. As a result, a housing is normally required to be attached above the casing head to provide room for the gearing and allow a rod to exit the tubing rotators of the prior art to allow manual rotation or automatic/continuous rotation of the tubing string.
These prior art designs therefore often include several seals to seal off the rod attached to the gears, seal the fluids between the casing and tubing, and further seal fluids produced up the tubing from exiting the tubing string into the atmosphere, ground, or annulus between the tubing and casing. The rotators with continuous rotation commonly have more corrosion holes due to wear than a manual or intermittent rotator, and fail when a gear mechanism fails and may damage the rotator or wellhead assembly due to the torque imparted on the gears. In addition, the positioning of a housing on top of the casing head is more costly and may involve the need to raise the pumping unit due to large spacing requirements between the casing head and the pump tee.
Wright U.S. Pat. No. 5,465,788 shows one prior art approach, a spline is used at 11 on the tubing hanger apparatus to allow one to attach a geared tubing rotator that will not fit within a Blow out protector “BOP” (thus, the reason for the spline design is to allow removal without turning the tubing). Wright's tubing hanger apparatus design and attached gear tubing rotator cannot all be removed or installed with the BOP stack attached to the wellhead. Further, the upper end of the tubing mandrel of Wright is disengaged from the tubing rotator through the application of force in a direction parallel to the longitudinal axis of the tubing string. This means a rig must be employed to pull the rotator assembly out of the tubing hanger to service the well. Further, Wright requires seals around the mandrel bowl and/or tubing mandrel to prevent communication between the high pressure fluids in the tubing and the low pressure fluids in the annular area surrounding the tubing. Failure of these seals leads to immediate pumping operation failure and loss of bearing lubrication and corrosion protection. Further, the rotator assembly attached to the tubing hanger has to be removed to change the conventional seals in Wright's design.
As will be seen from the subsequent description, the preferred embodiments of the present invention overcome these and other shortcomings of prior art.
There is need for a compact tubing rotator that may be operated manually or automatically to provide periodic and/or disproportionate rotation, reduces the height clearance between the casing head and the pump tee, is inexpensive, has minimal seals to potentially fail and leak fluids, provides for replacement of rubbers or seals that protect the atmosphere and environment from leaking fluids without removing the pump tee, the tubing rotator or tubing string from the well, provides additional seals to minimize or stop contamination of the grease packed bearing housing from wellbore or external fluids, utilizes commonly available equipment to reduce costs of repairs, and provides ease of installation and use.
The present invention is an apparatus for attachment within an existing casing head or within a casing head modified to accept a bowl or ledge assembly. In the preferred embodiment, this apparatus has a bearing in which a tubing mandrel rests and allows one to rotate the tubing manually above the wellhead. It provides a low profile reducing the distance between the casing head and the pumping tee, which may eliminate the need for one to raise the pumping unit to fit on the rotator. In addition, the conventional seals located above the bowl assembly have less chance of leaking fluids located between the casing and tubing as a result of the seals installed in the present invention. In addition, if the conventional rubber seal element starts to leak, then one can change the sealing elements without having to remove the pump tee, rotator assembly or tubing string from the well. In addition, some of the seals in the preferred embodiment can be changed without having to remove the pump tee, rotator assembly or tubing string from the well.